string::find

string (1)	size_t find (const string& str, size_t pos = 0) const noexcept;
c-string (2)	size_t find (const char* s, size_t pos = 0) const;
buffer (3)	size_t find (const char* s, size_t pos, size_type n) const;//n表示字符串s的前n个
character (4)	size_t find (char c, size_t pos = 0) const noexcept;

#include <iostream>
#include <string>

using namespace std;

int main()
{
string s1 = "i love lyy, i hope lyy can be married to me";
string s2 = "lyy";
cout << s1.find(s2) << endl;
cout << s1.find(s2, 50) << endl;
if(s1.find(s2, 50) == string::npos)
cout << "out_of_range" << endl;

const char *s3 = "lyy";
cout << "3: " << s1.find(s3, 8, 3) << endl;
cout << "4: " << s1.find('m', 6) << endl;
return 0;
}